This disclosure relates to the field of spinal fixation with screws and rods. While this type of fixation is frequently applied to the posterior aspect of the spine, there are times when screw and rod fixation may be applied to the lateral or anterior aspects of the spine. Fixation may include vertebrae, and may extend to the skull and/or the sacrum. Screw and rod fixation may be applied to the spine by securing screws in the spinal pedicles, vertebral bodies, sacrum, occiput, and so forth. Screw and rod fixation may also be applied to the rest of the skeleton.
This disclosure presents several examples of screw and rod systems, each of which provides at least two independent joints for angular movement between the central longitudinal axis of the screw and the central longitudinal axis of the rod. These examples may provide more angulation, or range of motion, than designs which incorporate only one joint. These examples may provide more than 50 degrees of angulation (half angle) at any rotational position of the screw relative to the rod, or in a preferred orientation of the screw relative to the rod. The joints disclosed herein may be hinge joints which permit rotation about an axis, ball and socket joints which permit multidirectional or polyaxial rotation about a point, or other types of joints or modifications thereof.